chore(cleanup): drop duplicate utils::purl::build_npm_purl

`utils::purl::build_npm_purl` was a byte-identical duplicate of
`crawlers::npm_crawler::build_npm_purl`. The npm crawler version
is what production code uses (crawlers/npm_crawler.rs:309 and
:656 in the discovery loops); nothing imported the utils one.

Removed the utils duplicate + its test. The npm-crawler version
keeps its own tests.

Workspace test sweep stays green (118 + 414 lib tests).

Assisted-by: Claude Code:claude-opus-4-7

Author: mikolalysenko

crates/socket-patch-core/src/utils/purl.rs

@@ -182,14 +182,6 @@ pub fn is_purl(s: &str) -> bool {
     s.starts_with("pkg:")
 }
 
-/// Build an npm PURL from components.
-pub fn build_npm_purl(namespace: Option<&str>, name: &str, version: &str) -> String {
-    match namespace {
-        Some(ns) => format!("pkg:npm/{}/{name}@{version}", ns),
-        None => format!("pkg:npm/{name}@{version}"),
-    }
-}
-
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -229,18 +221,6 @@ mod tests {
         assert!(!is_purl("CVE-2024-1234"));
     }
 
-    #[test]
-    fn test_build_npm_purl() {
-        assert_eq!(
-            build_npm_purl(None, "lodash", "4.17.21"),
-            "pkg:npm/lodash@4.17.21"
-        );
-        assert_eq!(
-            build_npm_purl(Some("@types"), "node", "20.0.0"),
-            "pkg:npm/@types/node@20.0.0"
-        );
-    }
-
     #[cfg(feature = "cargo")]
     #[test]
     fn test_parse_cargo_purl() {